Methods of making a mold



hire

No Drawing. Application June 25, 1952,

Serial No. 295,429 r 1 Claim. (Cl. 22-196) This invention relates to improvements in casting metals and more particularly to improved methods of producing decorative metal articles and of reproducing details of designs more clearly and accurately on metal surfaces.

In previously known processes it was common practice to make a rubber print of an original object, and in cases where the entire object was thereby enclosed in the rubber, it was necessary to cut this rubber in a special manner to extract the model or object. Wax was then applied to the printed surface and if the rubber print was a hollow form it was filled with the wax to provide a wax copy. A plaster casting of this wax copy was then made, and the wax was removed by burning, leaving a hollow casting of plaster with the imprint on the inner walls thereof. This hollow mold was then filled with molten metal generally by injection under highpressure. After hardening of the metal, the plaster was removed, thus leaving a metal copy of the original article.

In processes of the above type, the final copy is not generally as detailed as desired. Details of objects of nature such as leaves, flowers, etc., become obscure or obliterated, as the process progresses. In reproducing smooth-surfaced articles, the copy is not as smooth due to the pores of the plaster. Buffing is therefore required which adds to the labor, and to the cost. In copying complicated forms, it is difficult to remove the rubber, and with an increase in the cuttings in the rubber, the copy produced is less and less likely to be similar to the original. No amount of work on this copy can adequately serve to provide an accurate reproduction particularly of relatively minute details.

In the improved process of the present invention a high degree of accuracy in a copy is obtainable and more detailed reproduction with closer similarity is made possible principally by coating the surface design to be copied with metal, preferably by electroplating, and subsequently enclosing the metal-coated object in plaster, removing the object and utilizing the imprint on the electroplating metal for providing the design on a copy. It will be seen in the more detailed description of the process hereinbelow that the electroplating features, and others to be described, serve to provide highly desirable reproductions and improvements in the processes of producing them.

When a copy of an object is to be made or when a surface design on an object is to be reproduced, and if the object to be copied has no particular value and need not be preserved or recovered, the steps in the process may be as follows:

Example A 1. An end of a wax rod is attached to each of several spaced points on the surface of the object to be copied.

These rods serve in the formation of passages in the plaster casting to be applied in a subsequent step.

2. The object with the wax rods attached, is subjected to an electroplating process in which it is coated with a metal. If the object is made of metal, such as ordinary yellow brass (M. Pt. 940 C.), or copper (M. Pt. 1083 rates atcnt i 2,788,555 Patented Apr. 16, 1957 C.), or white metal (M. Pt. 238 C.), the metal used for electroplating should be of a higher melting point such as for instance nickel (M. Pt. 1452 C.), or chromium (M. Pt. 1615 C.), or platinum (M. Pt. 1755 C.). If the material of the object is combustible, the metal plating should not be fusible at the temperatures employed to reduce the object to ashes as explained in a succeeding step. If the object, such as an ornament that sets on a base, has a surface that is not ordinarily exposed to view, this surface need not be coated.

3. The. electroplated object and the attached rods are entirely enclosed in plaster as in a cast.

4. The resulting enclosed object is subjected to a tem perature high enough to remove the material of the object but below the fusion temperature of the metal deposited in the electroplating step. The material of the object, if combustible, is readily reduced to ashes, and if metal, the latter is fused. Upon heating the plaster cast, the wax rods will melt and the liquid wax will flow out of the aforesaid passages or will be removed by vaporization or burning, so that molten metal or products of combustion from the heat treatment of the object will also be removed through these passages. Ashes of a combusted object remaining in the cavity in the plaster may be removed by filling it with mercury, whereupon the ashes are floated off. The electroplating metal remains in the cavity on the surface of the walls thereof and bears the imprint of the shape or design of the original object.

If the original object is composed of metal and is fused in the cavity, the liquid metal may be removed from the cavity by centrifugalization.

5. The cavity in the plaster lined with the electroplating metal is filled with the metal (preferably of lower melting point than that of the plating) which composes the copy. This is done in various ways. In the present process it has been found highly efficient to draw the air out of the cavity, and to introduce the molten metal by centrifugal force. One way of accomplishing this is to place the plaster form and a container for the metal properly heated in a centrifugal chamber that is vacuumized. The arrangement is such that upon operation of the centrifuge the metal flows out of the container through the passages and into the cavity in the plaster form.

6. After the metal in the cavity has cooled sufiiciently to be hard, the plaster is removed, leaving the plated metal copy.

7. The plating metal is removed from the copy by electrolysis.

The copy thus produced is exactly identical with the original and its surface requires substantially no mechanical or other finishing treatment.

If a model to be copied is to be preserved in its original form and if the material of the original object is of such nature that the process of Example A is not suitable, then the following method is employed.

Example B 1. A rubber print is made of the original.

2. The original, if enclosed in the rubber, is extracted by cutting through it just enough to render possible the removal of the model.

3. The rubber serves as a mold for a wax casting.

4. The wax casting is coated with metal by electrolysis and the process is continued in accordance with the steps in Example A.

I claim:

In a method of reproduction by casting to provide accurate copies of close similarity to an object of nature, a succession of steps consisting of electroplating the surface of an original combustible object of nature having a surface design to be copied, investing the electroplated original object in plaster for a mold, removing by combustion the material of said object from the resulting mold, and removing residual ash of saidmaterial by introducing mercury and floating oft the ash to provide a cavity in said mold having on its Walls the electroplating metal with a direct imprint of the surface of the said original object, with which mold copies of said object are provided.

References Cited in the file of this patent UNITED STATES PATENTS Closson June 19, 1877 10 192,112 1,325,004 Davidson Dec. 16, 1916 1,377,372 Thompson May 10, 1921 1,416,412 Pack May 16, 1922 2,317,008 Werner Apr. 20, 1943 2,368,295 Goran Jan. 30, 1945 15 OTHER REFERENCES Skerritt: Scientific American, Feb. 26, 1916, p. 225. Steel, Mar. 19, 1951, pages 66-69 inclusive. 

